Throughout history, surveyors and mapmakers utilized immovable objects or monuments as reference points for the generated survey or map. Although these monuments were generally thought to be immobile, it has recently been determined that, due to the shifting of the earth's crust and similar movements, the actual latitude/longitude coordinates of these monuments have changed. The utilization of satellite positioning systems has indicated that several of these long-standing monuments have moved, in some cases several miles, since the initial determination of their latitude/longitude coordinates. Therefore, errors could result in constructing a survey or a map without periodically updating the exact latitude/longitude coordinates of the monuments.
Additionally, it has been determined that the present method of creating a map results in a map which is accurate to 50 feet in the center of the map and to 200 feet on the outside edges of the map. The reasons for these inaccuracies are not only due to the employment of inaccurately designated monuments, but rather to the methods utilized to create the modern-day map. Typically, maps have been created by aerial photography techniques, whereby an airplane would canvas, and take a plurality of photographs of, a certain geographic area. The largest inaccuracy resulting from this technique was that the angle of the camera and the lens utilized referenced to the surface of the earth would create distortions. This was true regardless of whether an actual or an infrared picture of the area was taken. Additional inaccuracies resulted since a flat map was created from a curved surface, thereby causing an inherent distortion of the map.
This aerial photography technique has largely been replaced by orbiting or geostationary satellites. The orbiting satellites would take a single sweep across an area, record an image and then take additional scans over adjacent areas, and images are produced in a manner such as that displayed on a television screen. However, regardless of the fact that a digitized image was being produced, a flat map was still being produced from a curved surface. Additionally, since the orbiting satellite was moving at a relatively great speed, further inaccuracies resulted. While a geostationary satellite would not produce inaccuracies due to the movement of the satellite relative to the earth, distortions due to the curvature of the earth were still produced.
Generally, if the mapmaker's purpose was to create a road or terrain map where the relative positions of roads, towns or physical formations were important, the distortion inaccuracies inherent in the mapmaking procedure were relatively unimportant, as long as the relative positions were consistent. However, quite recently, the need for tracking a particular vehicle and displaying the position of the vehicle on a digitized map more accurately than the distortion factor produced by state-of-the-art maps has been recognized. The Assignee of the present invention has developed a system, described in U.S. Pat. No. 4,651,157 for tracking a vehicle, and this application is incorporated by reference. One of the purposes of the invention described in the aforementioned application was to quite accurately track the position of a vehicle, such as a police car, taxi, ship or similar vehicle or vessel, as it traverses city streets or marine channels and rivers. The application describes a system in which a computer- generated digital map is provided on a display screen, and the position of the tracked vehicle is projected onto this map. Quite obviously, if the particular map is accurate to only 50 feet, the position of the tracked vehicle would not be accurately displayed on the projected map. Instead of the position of the automotive vehicle being properly shown on a particular street or road, the map might indicate that this vehicle is in the middle of a field or within a permanent structure, such as a building.
Therefore, a method of accurately displaying the position of the vehicle on a map, regardless of the inherent inaccuracy of the produced digitized map, must be developed. This display technique would then be able to be utilized in conjunction with the tracking system described in U.S. Pat. No. 4,651,157.